In packet-switched voice communication, maximum voice quality is achieved when voice packets arrive in the order that they were transmitted, at the exact rate that they are transmitted, and with the shortest possible transmission delay. However, the nature of data transmission in packet-switched or IP networks inherently gives rise to transmission delays (i.e. jitter) that may vary widely due to available bandwidth, number of nodes traversed by the packets, network congestion, etc. Packets can also be duplicated by network switching equipment or dropped. In addition, as a consequence of packet routing policies that are commonly employed, it is also possible for packets to arrive at an endpoint in a different order than they were transmitted.
It is known in the art to use data buffers when receiving voice packets, to ameliorate the effects of network jitter. For example, U.S. Pat. No. 6,603,749, entitled Adaptive Buffer Management for Voice Over Packet network, by Andre Moskal and Andre Diorio, discloses a fixed length adaptive buffer, wherein the length of the buffer is a compromise between introduced delay and induced packet loss due to underflow or overflow. The fixed length adaptive buffer is effective on well-conditioned networks. However, on less well managed networks (e.g. jitter greater than 40 ms) such as the Internet, the jitter often exceeds the size of the buffer. Consequently, the buffer actually introduces additional packet loss.
Accordingly, much research has centered on methods that dynamically adapt the buffer length according to current network conditions. Dynamic jitter buffers reduce the effects of variable transmission delay by introducing additional delay at the packet receiver. This has the benefit of requiring no special consideration at the packet transmitter. Dynamic jitter buffers reduce perceived network jitter by varying the amount of delay induced by the jitter buffer according to detected changes in network transmission delay.
Several approaches in the literature use adaptation to dynamically adjust the buffer to current changes in network delay. Adaptation techniques include LMS, neural networks, and fuzzy logic. Other methods use state machines, as set forth in Dynamic Jitter Buffering for Voice-Over-IP and Other Packet-Based Communication Systems (U.S. patent application Ser. No. 2003026275). Unfortunately, these tend to suffer from implementation complexities.